In-vessel retention (IVR) of core melt is a key severe-accident-management strategy adopted by some operating nuclear power plants and proposed for some advanced light water reactors (LWRs). If the...

In-Vessel Retention of Molten Corium: Lessons Learned and Outstanding Issues

One-dimensional critical heat flux concerning surface orientation and gap size effects

This article presents a comprehensive literature review on the fundamental issues of critical heat flux (CHF) during flow boiling and nucleate pool boiling in microscale channels and confined spaces. First, distinction between macro- and micro-scale channels is discussed. Then the CHF mechanisms are discussed. Next, experimental and theoretical studies of subcooled flow boiling CHF in microscale channels together with the prediction methods are reviewed and analyzed. Following this, experimental and theoretical studies on saturated flow boiling CHF together with the prediction methods are summarized and discussed. Furthermore, experimental and theoretical studies on nucleate pool boiling CHF in confined spaces together with the relevant prediction methods are reviewed as well. So far, limited studies on CHF microscale channels and confined spaces are available in the literature. There are numerous discrepancies in the existing studies on CHF results, mechanisms, and prediction methods. Furthermore, there ...

Fundamental Issues of Critical Heat Flux Phenomena During Flow Boiling in Microscale-Channels and Nucleate Pool Boiling in Confined Spaces

Experiments were performed to examine the pool boiling heat transfer and critical heat flux on a smooth copper circular surface, confined by a face-to-face parallel unheated surface, by changing both the orientation and the gap between the surfaces. Pool boiling data at atmospheric pressure were obtained for saturated HFE-7100. The gaps between the boiling surface and adiabatic one were 0.5, 1.0, 2.0, 3.5, 5.0, 10.0 and 20.0 mm. For each configuration, boiling curves were obtained up to the thermal crisis. The surface orientations investigated were 0° (horizontal upward surface), 45°, 90° and 135°. It was observed that the heat transfer coefficient improves at low wall superheat when the distance between heated and unheated surfaces decreases. However, at high wall superheat, a drastic reduction in heat transfer as well as CHF appears for confined boiling. For a fixed channel width, the CHF value strongly depends on the channel orientation, assuming a maximum value for near-vertical channels with up-facing heated surface. CHF data were compared with various literature correlations; a new empirical correlation that takes into account channel gap effects is proposed for horizontal confined surfaces.

Y. Kosho

Papers

Critical heat flux of saturated natural convection boiling in a space bounded by two horizontal co-axial disks and heated from below